1. Field of the Invention
This invention relates to a cutting tip which can be manufactured at low cost, and to the manufacture thereof.
2. Description of the Related Art
Generally, cutting tools are made by attaching a hard cutting tip to the end of a tool body. Cutting tip of this kind include for example the xe2x80x9cTwist Drillxe2x80x9d disclosed in Japanese Utility Model Laid-Open Publication No. HEI-5-63717 and the xe2x80x9cDrillxe2x80x9d disclosed in Japanese Utility Model Laid-Open Publication No. HEI-3-117520.
In the xe2x80x9cTwist Drillxe2x80x9d of Japanese Utility Model Laid-Open Publication No. HEI-5-63717, a wedge-shaped very high pressure sintered tip integrated with a cylindrical body part made from cemented carbide is used as the starting blank of a cutting edge body. This starting blank is fixed to a tool body by a method such as brazing, and the shape of an edge is formed to complete the cutting tool. However, in this xe2x80x9cTwist Drillxe2x80x9d, the starting blank is difficult to manufacture and is expensive. Consequently, as a result of the cost of the cutting tip being high, there has been the problem that the cutting tool is expensive.
In the xe2x80x9cDrillxe2x80x9d of Japanese Utility Model Laid-Open Publication No. HEI-3-117520, a drill is manufactured by cutting out a pentagonal tip blank from a disc made by surrounding a disc of cemented carbide with a ring-shaped a hard sintered compact. However, in the manufacture of this drill, from a disc of cemented carbide surrounded by a ring of a hard sintered compact, only from one to a few of the pentagonal tip blanks can be cut out, and the yield is poor. Consequently, not much effect of reducing the cost of the cutting tip or the cost of the cutting tool can be expected.
FIGS. 59A through 59C illustrate a typical thread-cutting method of related art.
FIG. 59A: A drill 512 is set in a machine tool 510; the drill 512 is aligned with a cored hole 511, and machining of a prepared hole is started. The point angle xcex8 of the drill 512 is 120xc2x0 in general.
FIG. 59B: Next, the drill 512 is replaced with a tap 514 for thread-cutting. The reference numeral 513 denotes the prepared hole made with the drill 512, and its depth is D1. The tap 514 is aligned with this prepared hole 513 and thread-cutting is started.
FIG. 59C: The reference numeral 515 denotes a female thread formed by the tap 514. The tap 514 is replaced with a chamfering tool 516, and the entrance of the thread 515 is chamfered with the chamfering tool 516. The reference numeral 517 denotes the chamfer. If the length of the thread 515 including this chamfer 517 is written D2, then an unthreaded part of length (D1-D2) remains.
In this thread-cutting method of related art, to form the thread 515, a drill, a tap and a chamfering tool are necessary; thus the number of tools required is large, tool supply costs are high and tool management costs are high. Also, it is necessary for tools to be interchanged during the process from the hole-making to the chamfering. Because of this, the cutting work must be stopped for every tool change, the thread-cutting machining operation is troublesome, and there are problems of productivity.
Also, because an unthreaded part of length (D1-D2) is unavoidable, the unthreaded part must be allowed for in the casting, and consequently there has been the problem that it is not possible to make the casting thin.
Next, as the cutting tool for finishing the hole, generally a reamer is used, to finish the opened hole in advance exactly and obtain a smooth finished surface at the same time. By machining the hole with a reamer, an accurate hole can be obtained. As the procedure for finishing a hole with a reamer, first a small-diameter hole is made with a drill, and then by dragging the wall of the hole with the reamer the hole diameter is finished to the required accuracy (for example, dimensional accuracy H7 (JIS B 0401).
Thus, a reamer is necessary to obtain an accurate hole; however, with this finishing method, the number of tools required is large, numerous tools have to be set on and removed from the machine tool, and preparation is troublesome. Also, hole-finishing with a reamer takes time, and it is necessary for machining with the machine tool to be stopped for the tool change from the drill to the reamer to be carried out. Consequently, the productivity of the hole-machining is low.
It is therefore a first object of the present invention to provide an inexpensive cutting tip and cutting tool and a method by which this cutting tool can be manufactured.
It is a second object of the invention to provide a thread-cutting method with which it is possible to reduce the number of tools required for thread-cutting and to dispense with an unthreaded part.
It is a third object of the invention to provide a hole-finishing drill which allows good productivity.
According to a first aspect of the present invention, there is provided a cutting tip having a first layer consisting of a cemented carbide tool material, a second layer consisting of a hard sintered compact of CBN or diamond, and a third layer consisting of a cemented carbide tool material; the second layer is sandwiched by the first layer and the third layer to form a three-layer laminate, and a cutting edge is formed in the second layer.
Because the cutting tip as a whole is a three-layer structure, and the second layer is reinforced on both sides by the first layer and the third layer, the rigidity of the tip increases.
According to a second aspect of the present invention, there is provided a method for manufacturing a cutting tip, the method including a preparation step of preparing a three-layer laminate wherein a second layer consisting of a hard sintered compact of CBN or diamond is sandwiched by a first layer and a third layer consisting of a tool material such as cemented carbide, a first cutting step of cutting out a prismatic blank of rectangular cross-section by cutting the first layer, the second layer and the third layer in order substantially perpendicularly to the upper face of the first layer, a second cutting step of cutting out a semi-completed tip including the second layer in the middle thereof by cutting from one cut face of the prismatic blank to the other cut face, and a finishing step of obtaining a completed tip by forming on the semi-completed tip a rake face, a cutting edge and a flank.
Because the three-layer laminate is cut in strips and semi-completed tips are cut out from the prismatic blanks obtained, semi-completed tips can be obtained in large numbers. Consequently yield is good, and the manufacturing cost of the tip can be greatly reduced.
According to a third aspect of the present invention, there is provided a cutting tool made up of a shank and a tip attached to the shank, wherein the tip is made from a three-layer laminate wherein a second layer consisting of a hard sintered compact of CBN or diamond is sandwiched by a first layer and a third layer consisting of a tool material such as cemented carbide, and when the cutting tool is seen in front view, the second layer is a narrow band passing through the center of rotation of the tool, a cutting edge is formed in this narrow band, and the second layer is reinforced on both sides by the first layer and the third layer.
If an oil passage is formed in the shank and another oil passage is formed in the second layer of the tip and the two oil passages connect in a straight line, cutting oil can be injected through the oil passages at the time of cutting. And these holes can be utilized as positioning parts when the tip is attached to the shank.
According to a fourth aspect of the present invention, there is provided a method for manufacturing a cutting tool made up of a shank and a tip attached to the shank, the method including a preparation step of preparing a three-layer laminate wherein a second layer consisting of a hard sintered compact of CBN or diamond is sandwiched by a first layer and a third layer consisting of a tool material such as cemented carbide, a first cutting step of cutting out a prismatic blank of rectangular cross-section by cutting the first layer, the second layer and the third layer in order substantially perpendicularly to the upper face of the first layer, a second cutting step of cutting out a semi-completed tip including the second layer in the middle thereof by cutting from one cut face of the prismatic blank to the other cut face, a joining step of joining the semi-completed tip to a separately prepared shank, and a finishing step of obtaining a completed tip by forming on the semi-completed tip a rake face, a cutting edge and a flank.
Thus, cutting tools are obtained by cutting a three-layer laminate in strips, cutting out numerous semi-completed tips from the prismatic blanks obtained, attaching the semi-completed tips to shanks, and finishing the tips. Consequently, because yield is extremely good and the manufacturing cost of the tips can be greatly reduced, the manufacturing cost of the cutting tool can be reduced.
Preferably, oil passages are made in advance in the shank and in the semi-completed tip and in the joining step the semi-completed tip is positioned on the shank by a pin being passed through the two holes and joining of the semi-completed tip and the shank is carried out in this state. Because the semi-completed tip can be positioned with respect to the shank by a pin being passed through the two oil passages like this, a cutting tool having good dimensional accuracy can be manufactured easily.
According to a fifth aspect of the present invention, there is provided a method for manufacturing a cutting tip, the method including a preparation step of preparing a three-layer laminate wherein a second layer consisting of a hard sintered compact of CBN or diamond is sandwiched by a first layer and a third layer consisting of a tool material such as cemented carbide, a first cutting step of cutting out a prismatic blank of rectangular cross-section by cutting the first layer, the second layer and the third layer in order substantially perpendicularly from the upper face of the first layer, a second cutting step of cutting out a semi-completed tip including the second layer in the middle thereof by cutting the prismatic blank on a cutting plane orthogonal to or inclined at a predetermined angle to the cut face of the first cutting step, and a finishing step of obtaining a completed tip by forming on the semi-completed tip a rake face, a cutting edge and a flank.
According to a sixth aspect of the present invention, there is provided a method for manufacturing a cutting tool made up of a shank and a tip attached to the shank, the method including a preparation step of preparing a three-layer laminate wherein a second layer consisting of a hard sintered compact of CBN or diamond is sandwiched by a first layer and a third layer consisting of a tool material such as cemented carbide, a first cutting step of cutting out a prismatic blank of rectangular cross-section by cutting the first layer, the second layer and the third layer in order substantially perpendicularly to the upper face of the first layer, a second cutting step of cutting out a semi-completed tip including the second layer in the middle thereof by cutting the prismatic blank on a cutting plane orthogonal to or inclined at a predetermined angle to a cut face of the first cutting step, a joining step of joining the semi-completed tip to a separately prepared shank, and a finishing step of obtaining a completed tip by forming on the semi-completed tip a rake face, a cutting edge and a flank.
According to a seventh aspect of the present invention, there is provided a thread-cutting tool made up of a shank and a tip attached to the shank, wherein the tip is made up of a three-layer laminate in which a second layer consisting of a hard sintered compact of CBN or diamond is sandwiched by a first layer and a third layer consisting of a tool material such as cemented carbide, and, when the thread-cutting tool is seen in front view, the second layer is a thin band passing through the center of rotation of the tool, an end cutting edge and a thread-cutting edge are formed in this narrow band, and the second layer is reinforced on both sides by the first layer and the third layer.
A prepared hole is made with the end cutting edge of the thread-cutting tool, and thread-cutting is carried out with the thread-cutting edge. Because chamfering is also possible with the thread-cutting edge and the end cutting edge, the thread-cutting process can be carried out with a single tool. This single thread-cutting tool is obtained by cutting a three-layer laminate along parallel lines, cutting out numerous semi-completed tips from the prismatic blanks thus obtained, attaching these semi-completed tips to shanks, and finishing the tips. Accordingly, yield is good and the manufacturing cost of the thread-cutting tool can be reduced.
A flat drag of smaller diameter than the thread-cutting edge and larger diameter than the shank is formed on the side of the tip attached to the shank, and the end cutting edge, the thread-cutting edge and the flat drag are formed in this order in the second layer. While a thread is being cut with the thread-cutting edge, the rake simultaneously cuts flat the crests of the thread ridges, and the bottom of the threaded hole is finished by the end cutting edge. The reason for cutting the crests of the thread ridges is to prevent the shank from making contact with the thread ridges.
An oil passage is formed in the shank and an oil passage is formed in the second layer of the tip, and the two oil passages connect in a straight line. When thread-cutting is carried out, cutting oil is injected through the oil passages.
According to an eighth aspect of the present invention, there is provided a method for cutting a thread using a thread-cutting tool, the method including a prepared hole machining step of making a prepared hole of substantially the same diameter as the external diameter of the thread-cutting tool by passing the thread-cutting tool into a cored hole while rotating it about a threaded hole axis, an offsetting step of offsetting the axis of the thread-cutting tool from the threaded hole axis by a predetermined distance after the end of the thread-cutting tool reaches the bottom of the prepared hole and starting thread-cutting in the prepared hole with a thread-cutting edge formed on the tool, and a thread-cutting step of cutting a thread with the thread-cutting edge by rotating the axis of the thread-cutting tool about the threaded hole axis while gradually withdrawing the thread-cutting tool in correspondence with the lead of the thread.
Because the bottom of the threaded hole is finished at the same time as the prepared hole is made with an end cutting edge, the depth of the prepared hole and the thread depth become essentially the same, and it is possible to dispense with an unthreaded part.
According to a ninth aspect of the present invention, there is provided a method for cutting a thread using a thread-cutting tool, the method including a thread-cutting step of cutting a thread in a cored hole with a thread-cutting edge by offsetting the axis of the thread-cutting tool from the threaded hole axis by a predetermined distance and then turning the thread-cutting tool about the threaded hole axis and rotating the thread-cutting tool and advancing the thread-cutting tool in correspondence with the lead of the thread, a thread ridge dragging step of dragging with a flat drag formed on the thread-cutting tool the crests of the ridges of the thread cut out with the thread-cutting edge, and a bottom finishing step of finishing with an end cutting edge formed on the thread-cutting tool the bottom of the threaded hole.
By this means it is possible to carry out thread-cutting with an advancing movement of a thread-cutting tool without making a prepared hole in a cored hole. And because after the thread-cutting it is only necessary to remove the tool, the time required for thread-cutting can be shortened.
According to a tenth aspect of the present invention, there is provided a thread-cutting tool made up of a shank and a tip attached to the shank, wherein the tip is made up of a three-layer laminate in which a second layer consisting of a hard sintered compact of CBN or diamond is sandwiched by a first layer and a third layer consisting of a tool material such as cemented carbide, and, when the thread-cutting tool is seen in front view, the second layer is a thin band passing through the center of rotation of the tool, a drill edge and a thread-cutting edge are formed in this narrow band, and the second layer is reinforced on both sides by the first layer and the third layer.
A prepared hole is made with the drill edge of the thread-cutting tool, thread-cutting is carried out with the thread-cutting edge of the thread-cutting tool, and because chamfering is also possible with the drill edge, the thread-cutting process can be carried out with a single tool.
At least two oil passages are provided in the shank, and to face these oil passages at least one oil passage is provided in each of the first layer and the third layer of the tip so that the oil passages in the shank and the oil passages in the tip are connected. When a plurality of oil passages are provided in this way, more cutting oil can be injected, and thread-cutting can be carried out smoothly.
According to an eleventh aspect of the present invention, there is provided a thread-cutting method including a prepared hole machining step of making a prepared hole in a workpiece with a drill edge formed on a thread-cutting tool by rotating the thread-cutting tool about a threaded hole axis, an offsetting step of offsetting the axis of the thread-cutting tool from the threaded hole axis by a predetermined distance after the thread-cutting tool reaches the bottom of the prepared hole and starting thread-cutting in the prepared hole with a thread-cutting edge formed on the thread-cutting tool, and a thread-cutting step of cutting a thread with the thread-cutting edge by rotating the axis of the thread-cutting tool about the threaded hole axis while gradually withdrawing the thread-cutting tool in correspondence with the lead of the thread.
According to a twelfth aspect of the present invention, there is provided a method for cutting a thread using a thread-cutting tool, which method comprises the steps of: making a prepared through hole in a workpiece with a drill edge formed on a thread-cutting tool by rotating the thread-cutting tool about a threaded hole axis; chamfering an outlet of the prepared through hole with a back of the drill edge; offsetting a center axis of the thread-cutting tool from a threaded hole axis by a predetermined distance for cutting a thread in the prepared through hole with a thread-cutting edge formed on the thread-cutting tool; and cutting a thread in the through hole with the thread-cutting edge by gradually pulling the thread-cutting tool out from the hole in correspondence with a lead of the thread while rotating the axis of the thread-cutting tool about the threaded hole axis.
In this arrangement, the prepared through hole is first formed in the workpiece by means of the drill edge. At this time, a burr is produced at a peripheral edge of an outlet of the prepared through hole. Then, a chamfer is provided at the outlet by using the back of the drill edge (part of the thread-cutting edge). The burr is removed upon chamfering. Continuously, thread cutting is performed on the prepared through hole upwardly from the outlet. In this arrangement, only a single tool is thus required to achieve the prepared through hole machining, chamfering and thread cutting.
According to a thirteenth aspect of the present invention, there is provided a hole-finishing drill made up of a shank and a tip attached to the shank, wherein the tip is made up of a three-layer laminate wherein a second layer consisting of a hard sintered compact of CBN or diamond is sandwiched by a first layer and a third layer consisting of a tool material such as cemented carbide; when the drill is seen in front view, the second layer is a thin band passing through the center of rotation of the tool, a cutting edge is formed in this narrow band, and a pair of lands are formed on the periphery of the tip; the cutting edge is a stepped edge formed with a plurality of steps in the form of a stairway radially outward from the drill center; and guide pads for preventing run out of the tip are formed projecting on the lands of the drill.
Because the cutting edge is stepped, chips are broken up finely. Consequently, a chip discharge groove formed in the drill can be made small, and the rigidity of the drill can be increased. Since the guide pads formed on lands of the drill make contact with the wall face of the hole, run out of the tip is prevented, the wall face is cut smoothly, and the dimensional accuracy of the hole increases. In this way, a hole-making process and a finishing process can be carried out with a single drill.
According to a fourteenth aspect of the present invention, there is provided a cutting tool made up of a shank and a tip attached to the shank, wherein the tip is made up of a three-layer laminate wherein a second layer consisting of a hard sintered compact of CBN or diamond is sandwiched by a first layer and a third layer consisting of a tool material such as cemented carbide; when the cutting tool is seen in front view, the second layer is a thin band passing through the center of rotation of the tool, and a cutting edge is formed in this narrow band; and an end cutting edge constructed in the form of a stairway to keep chips small, a thread-cutting edge for cutting a thread, and a flat drag the same diameter as the internal diameter of the female thread are formed in the cutting edge in this order from the end of the tip toward the shank.
The tip has an end cutting edge having a plurality of steps, a thread-cutting edge and a flat drag. A chamfering process is carried out in advance by the thread-cutting edge. A hole-preparing process is carried out by the end cutting edge and the thread-cutting edge. Crests of ridges of a female thread having a predetermined internal diameter are formed by the flat drag the same diameter as the internal diameter of the female thread. Because a chamfer formed at the opening of the threaded hole is made in advance like this, when the thread-cutting process ends there is no formation of a burr at the threaded hole opening, and means for removing a burr are not necessary. Thus in this invention, machining of a chamfer, hole-preparing, thread-cutting, and machining of thread ridges can be carried out with a single cutting tool. As a result, there is no need for tool changes, and cutting work can be carried out continuously, without stopping.